Antennas are used for the radiation and capture of electromagnetic energy. For example, a wireless communications system typically includes one or more antennas on each node within the system. Improved link performance can sometimes be obtained by using antennas which focus or concentrate radiated energy in a particular direction. In particular, by focusing radiated energy (e.g., within a narrow beamwidth) toward a node being transmitted to, rather than sending energy in all directions (e.g., isotropically), the resulting increase in energy can translate into improved link performance (e.g., lower error rate, higher signal quality, increased range, etc.). Such antennas are referred to as directional antennas. Because antennas can operate in a reciprocal manner, similar performance gains can be obtained when using a directional antenna for transmitting or receiving.
There is a tradeoff, however, when using directional antennas. If the antenna is not pointed directly at the other end of the communications link, performance gains can be lost, and performance can even be worse than using an isotropic antenna. Accordingly, it is helpful to provide techniques to ensure that the antenna is correctly pointed. When one or both ends of the communications link are moving, maintaining correct antenna pointing can be difficult.
One approach to maintaining antenna pointing is to perform tracking, where measurements of the signal are used to determine whether the antenna is pointing correctly. Tracking systems to date have failed to provide the desired cost, performance, and other characteristics. In particular, tracking systems are often bulky, resulting in undesirable weight. Bulky tracking systems can also cause undesired blockage of the antenna aperture. Blockage can be particularly problematic in multi-band antenna feeds.